The present invention relates generally to zoom lenses, and particularly to a zoom lens which can be actuated to perform close up photography at either the telephoto end or the wide angle end of the range of its optical system.
Zoom lens barrels which can be used for close up photography are known, an example being disclosed in U.S. Pat. No. 3,613,544. A cylindrical guide member is typically used to control movement of the optical system in the zoom lens barrel so as to properly vary the magnification factor, and a guide groove in the guide member, which engages a cam, serves to select a close up photographing range when the guide member is rotated about the lens barrel axis. The guide is usually formed as an extension of the groove provided in the guide member which corresponds to the zoom photographing range. However, such an arrangement has the disadvantage that the overall length of the guide groove becomes undesirably long. This is so because, in order to enable zoom photography to be carried out smoothly by rotation of the cylindrical guide member, several guide grooves must be provided in the circumferential surface of the guide member, each groove serving to transfer movement to one of a number of lens systems in the barrel. When the length of a guide groove is too long, the distance between adjacent guide grooves in the guide member becomes relatively small, giving rise to poor accuracy and the possibility of deformation of the guide member during manufacture. While these disadvantages may be overcome by increasing the wall thickness or axial length of the guide member, such dimensional changes will increase the overall diameter and/or length of the lens barrel, so that such changes are not a desirable countermeasure.
Further, U.S. Pat. No. 4,099,847 discloses the use of a cylindrical guide member, which is engaged in a fixed portion of the lens barrel, to control movement of the lens systems in the barrel between a zoom photographing range and a close up photographing range. In lens barrels capable of both zoom photography and close up photography, the lens systems are moved in the lens barrel in the direction of the optical axis in order to focus on an object to be photographed. A number of lens systems for providing variation of the magnification factor and for optical compensation are thus moved by following guide surfaces or grooves formed in the cylindrical guide member as the guide member is rotated.
Consequently, the positioning of the guide member on the lens barrel is most important. However, since the guide member is usually arranged either on an internal or external surface of a fixed part of the lens barrel, adjustment of its position from the outside, particularly along the direction of the optical axis, is extremely difficult. Thus, it is difficult to accurately control the optical distance between the principal point of the lens systems and the standard position for the lens barrel mount. This results in a lower efficiency for the zoom lens.
An object of the present invention is to eliminate the above-mentioned shortcomings in the conventional zoom lenses, and to enable close up photography without the necessity of providing a guide member groove which is an extension of the guide groove provided for the zoom photographing range.
Another object of the present invention is to provide a zoom lens capable of close up photography at both the telephoto and the wide angle ends of the range of the lens barrel optical systems, as well as at any point within the operational range of the lens.
A further object of the present invention is to provide a zoom lens which can be placed into a close up photography mode of operation by way of an operating member which is separate from the focusing and zoom operation members to avoid misoperation while a photographer is taking a picture in the ordinary zoom photographing range.
Yet another object of the present invention is to provide an adjustable, high precision zoom lens barrel which can be easily assembled wherein the position of the cylindrical guide member on the lens barrel can be adjusted in the direction of the optical axis of the lens barrel to change over between the zoom and close up photography operating modes.
In accordance with the present invention, a zoom lens barrel for use in zoom and close up photography includes a cylindrical barrel part one end of which is arranged to be mounted on a camera body. An optical system is provided within the barrel part for performing zoom and close up photography, the system having an optical axis which coincides with the axis of the barrel part and being arranged for axial sliding movement relative to the barrel part. A generally cylindrical guide member is coaxially rotatably mounted on the barrel part, the guide member having a number of guide slots for engaging the optical system and a guide edge formed on one end of the guide member. The guide member is axially movable between a first position whereat the guide slots axially guide the optical means relative to the barrel part so that the system zooms on an object to be photographed when the guide member is rotated, and a second position whereat the guide member axially displaces the optical system for close up photography of the object. An operation member is mounted on the barrel part nest to the guide edge on the guide member for engaging the guide edge to move the guide member axially between the first and second positions.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention .